North Korea does not yet have an operational missile that could hit the continental US, a US report says.

But its weapons could target South Korea and Japan, and it is working on a longer-range solid-fuel missile.

Missile exports were a significant source of foreign exchange for the country, the report by the Center for Nonproliferation Studies also said.

Concerns over North Korea's weapons programme rose this month when it test-fired two short-range missiles.

A US military official told a government committee that the missiles represented a "leap forward" for Pyongyang's programme in terms of reliability and accuracy.

'Several years'

The report by the California-based NGO said that North Korea did not currently have "an operational missile" to strike the US.

The longer-range Taepodong-X missile could theoretically reach Alaska, Hawaii and parts of the coastal US, US officials believe, and an untested third version, Taepodong 2, could potentially strike further into the country.

But the report said the missile would not be accurate and the payloads it could carry would be militarily insignificant.

"North Korea has not demonstrated the capability to make a nuclear weapon small enough to be part of a missile warhead," the report said.

Pyongyang would require "several years" to produce a reliable missile system that could deliver a nuclear warhead to the US, it said.

Exports to Iran

But the NGO said North Korea had more than 800 ballistic missiles and could reach South Korea and Japan with possible biological and chemical payloads.

It has a Scud-type missile with which it could target all of South Korea, and it has missiles with a range of 1,000 km (625 miles) with which it could strike Japan.